Polymers of lower α-alkene or olefins such as ethylene, propylene or 1-butene find applications in the manufacture of a variety of articles including plastic bags or sheets or automobile parts. Of particular interest in polymer production are polyethylene and polypropylene with a high degree of isotacticity i.e. the extent of orientation of the branched groups in the polymer in the same direction, which shows high crystallinity. The polymerisation involves reacting the lower α-alkene such as ethylene or propylene with catalyst under polymerisation conditions. The early polymerisation on catalysts were of relatively low activity and the polymers formed contained significant amounts of the catalyst residues, which had to be removed by deashing. The more recent alkene polymerisation catalysts are of two types viz. single site catalysts and heterogeneous solid catalysts. The single site catalysts comprise metallocene and non-metallocene complexes of transition metals and a cocatalyst such as methyl aluminoxane and produces polymer of low polydispersity.
Heterogeneous solid catalysts are the most commonly used catalysts, especially in the bulk production of polyethylene or polypropylene due to their high activity and ease of operation. These catalysts are sometimes referred to as heterogeneous Ziegler-Natta catalysts. A heterogeneous solid catalyst comprises a procatalyst and a cocatalyst and for polypropylene with high isotacticity an external selectivity control agent or external electron donor also. The cocatalyst may be an organoaluminium compound such as alkyl aluminium. The physicochemical properties of the procatalyst play a pivotal role in the overall performance of the catalysts. The procatalysts comprise organomagnesium or magnesium chloride derived precursor comprising magnesium chloride supported titanium chloride and an internal electron donor. The procatalysts are synthesised by halogenation of an organomagnesium compound such as magnesium ethoxide with a halogenating agent such as titanium tetrahalide in a hydrocarbon or halohydrocarbon solvent such as toluene or chlorobenzene optionally with an acid halide to form magnesium chloride. The magnesium chloride so obtained is reacted with titanium haloalkoxide or excess titanium tetrahalide, usually titanium tetrachloride in the presence of a hydrocarbon or a halohydrocarbon solvent. To this an internal electron donor is added simultaneously or sequentially to result in a procatalyst U.S. Pat. Nos. 4,400,302, 4,414,132, 4,497,905, 4,535,068, 4,657,995, 4,710,482, 4,728,705, 4,771,024, 4,804,648, 4,870,039, 4,914,069, 4,870,040, 5,066,737, 5,077,357, 5,106,806, 5,082,907, 5,122,494, 5,124,298, 5,141,910, 5,151,399 and 5,229,342. In most of the above processes employing organomagnesium compounds or silica coated with organomagnesium compounds, the procatalyst preparation involves treatment of the magnesium precursor with titanium tetrahalide more than once, so that catalysts of optimum titanium loading and activity are obtained. U.S. Pat. Nos. 4,400,302 and 4,414,132 teach that at least two treatments with titanium tetrahalide are required for catalysts with high activity. In U.S. Pat. Nos. 4,497,905, 4,535,068 and 4,657,995, where a halogenating agent is used to enhance activity, several treatments with titanium tetrachloride are described. The total amount of titanium tetrahalide required for multiple treatments are also considerable.
Procatalyst also may be prepared by milling together anhydrous magnesium chloride, a titanium tetrahalide such as titanium tetrachloride and for polypropylene catalyst an internal electron donor U.S. Pat. Nos. 4,329,253, 4,393,182 and 4,419,501. Preparation of procatalysts by this physical method requires very long milling time. Furthermore when used in polymerisation reactions, procatalysts obtained by milling in general show activities and selectivities inferior to those obtained by chemical method.
Several processes and products employing microwave energy are reported in patent literatures. PCT Publication No WO2001028771 describes microwave curable compositions comprising at least one heat curable resin component, microwave absorbable particles in an amount of about 10% of the composition, and at least one curing agent for the heat curable resin component. European Patent no 992480 describes the preparation of methacrylate and polyester methacrylates in the presence of a catalyst and inhibitor under microwave heating. U.S. Pat. Nos. 6,017,845 and 6,171,479 describe a process that involves a catalyst comprising a support, a microwave absorption material and catalytically active phase. On heating the catalyst with a source of microwave energy, the microwave absorption material absorbs the energy and increases the temperature of the catalyst to the desired level. The heated catalyst is contacted with a hydrocarbon feedstock for upgrading. PCT Publication No WO 9743230 describes a method for palladium catalyzed organic reactions heated with microwave energy in solution. U.S. Pat. No. 5,194,514 describes the use of microwave in the presence of paramagnetic catalysts to increase molecular weight of the polymer. U.S. Pat. No. 5,719,095 describes supported catalyst system comprising support, at least one metallocene catalyst fixed to the support, and at least one cocatalyst, wherein the catalyst is fixed to the support by bringing the catalyst into contact with a supported cocatalyst in a suspension and irradiating with microwaves.